In the residential renovation market, replacing windows and doors is often presented as the obvious way to improve thermal performance in an older home. That approach, while commercially effective, overlooks the heritage value of original millwork and underestimates restoration possibilities. Studies carried out in several Canadian provinces indicate that properly restored sash windows in solid wood, fitted with a storm window, can achieve performance comparable to modern double-glazed units.
The Sash Window: A Durable Construction Logic
The sash window is the dominant window type in Canadian heritage homes built between 1820 and 1930. It consists of two vertically sliding frames held in position by a counterweight system concealed in the side jambs.
Original Materials
Old sashes are made of white pine, spruce, or hemlock — dense, tight-grain woods resistant to deformation and rot when surface maintenance is maintained. These species are significantly more stable than plantation wood used today.
Common Failure Points
- Worn or broken counterweight cords (causing sashes that will not stay in position)
- Dry, cracked, or detached glazing putty (linseed oil mastic)
- Rot at lower sash corners in prolonged contact with moisture
- Accumulated paint layers blocking sash movement
- Missing or damaged interior glazing bars and mouldings
Most of these problems are repairable without replacing the entire window.
Restoration Protocol for a Sash Window
1. Removal and Assessment
The window must be removed from its frame for proper assessment. Sashes are taken out by removing interior glazing bars. Each piece is inspected for rot, cracks, and glazing condition.
2. Treatment of Degraded Wood
Areas of light to moderate rot can be treated with liquid epoxy consolidants, followed by mouldable epoxy fill. This technique restores wood shape and rigidity without replacing entire pieces. Sections that are too degraded are replaced with inserts of the same species and grain orientation.
3. Counterweight Cord Replacement
Original cotton or hemp cords are replaced with braided synthetic cord (polyester or Dacron) that does not decompose. This operation requires opening side frame panels to access pulleys and counterweights.
4. Glazing Resealing
Traditional linseed oil putty remains the reference material for old glazing. It adheres better to glass and wood than synthetic compounds on painted frames. After application and smoothing, it must dry for several weeks before painting.
Heritage Doors
Exterior doors on Canadian heritage homes are generally solid wood (pine, oak, or walnut depending on the standing of the residence), with raised-and-fielded panels and upper glazing. Their mass and thickness — often 5 to 6 cm — make them naturally more insulating than modern hollow doors.
Common Problems
- Warping due to humidity variation (seasonal swelling and shrinkage)
- Open joints between panels in dry seasons
- Seized or missing hardware (hinges, latches, locks)
- Rotten wood thresholds in contact with damp ground
Conservation Solutions
Minor warping can be corrected by balancing humidity (coat all faces, including edges, to uniformize absorption). Joints between panels are filled with flexible linseed oil compound or fine wood splines. Period hardware — rim locks, forged hinges — can be cleaned, lubricated, and reinstalled; faithful reproductions are available from specialized ironmongers.
Appropriate Weatherstripping and Sealing
One of the most effective improvements for reducing air infiltration around old windows and doors is installing discreet weatherstripping. Spring bronze models, which can last several decades, are compatible with older millwork and do not alter appearance. They are available from specialized hardware suppliers or heritage material vendors.